Nobody knows the true identity of "Hard Harry" or "Happy Harry Hard-on," as Mark refers to himself, until Nora Diniro, a fellow student, tracks him down and confronts him the day after a student named Malcolm commits suicide after Harry attempts to reason with him. The radio show becomes increasingly popular and influential after Harry confronts the suicide head-on, exhorting his listeners to do something about their problems instead of surrendering to them through suicide—at the crescendo of his yelled speech, an overachieving student named Paige Woodward (who has been a constant listener) jams her various medals and accolades into a microwave and turns it on. She then sits, watching the awards cook until the microwave explodes, injuring her. While this is happening, other students act out in cathartic release.

Eventually, the radio show causes so much trouble in the community that the FCC is called in to investigate. During the fracas, it is revealed that the school's principal has been expelling "problem students," namely, students with below-average standardized test scores, in an effort to boost the district's test scores while still keeping their names on the rolls (a criminal offense) in order to retain government funding.

Realizing he has started something huge, Mark decides it is up to him to end it. He dismantles his radio station and attaches it to his mother's old jeep, creating a mobile transmitter so his position can't be triangulated. Pursued by the police and the FCC, Nora drives the jeep around while Mark broadcasts. The harmonizer he uses to disguise his voice breaks, and with no time left to fix it, Mark decides to broadcast his final message as himself. They finally drive up to the crowd of protesting students, and Mark tells them that the world belongs to them and that they should make their own future. The police step in and arrest Mark and Nora. As they are taken away, Mark reminds the students to "talk hard." As the film ends, the voices of other students (and even one of the teachers) speak as intros for their own independent stations, which can be heard broadcasting across the country.

After his film Times Square, a new wave comedy, was taken away from him and re-edited, Allan Moyle retired from directing and began working on screenplays. One of them, about a teenager who runs his own pirate radio station for other teenagers, came to the attention of SC Entertainment, a Toronto-based company, and put into development.[2] He was persuaded to direct his own screenplay. Moyle wrote it without a specific actor in mind but his development deal specified that the project would be canceled if a suitable actor could not be found. The director needed an actor who had to have "glee, to be ineffably sweet and at the same time demonic."[2] Christian Slater met with Moyle and producer Sandy Stern and displayed all these qualities. Moyle has described the film's protagonist as an amalgam of Holden Caulfield and Lenny Bruce[2] and the "Hard Harry" persona as a guy who "has to get credibility as an outsider. As the last angry man on the planet, he has to use the foulest language he can think of. He even pretends to masturbate on the air. He's obsessed with sex and death."[3] The school in the film, Hubert Humphrey High, was based on a Montreal high school where director Allan Moyle's sister used to teach that, according to Moyle, had a principal "who had a pact with the staff to enhance the credibility of the school scholastically at the expense of the students who were immigrants or culturally disabled in some way or another."[3]

Slater disagreed with Moyle who wanted to bring in a tap dance instructor to help orchestrate a scene that begins with "Hard Harry" faking masturbation on the air and ends with him breaking into a manic dance by himself. Slater wanted to do something more spontaneous based on his instincts.[4]

Pump Up the Volume failed to catch on at the box office. When it was released on August 24, 1990, in 799 theaters, it grossed USD $1.6 million in its opening weekend. It went on to make $11.5 million in North America.[5]

The film received generally positive reviews from critics and is currently rated 79% at Rotten Tomatoes based on 33 reviews. In his review for the New York Times, Stephen Holden wrote, "Much like Heathers, Pump Up the Volume doesn't know how to draw out its premise, once that premise has been thoroughly explored. As the film accelerates toward its conclusion, the strands of its clever plot are too hastily and perfunctorily resolved . . . Working within the confines of the teen-age genre film, however, Pump Up the Volume still succeeds in sounding a surprising number of honest, heartfelt notes".[6]USA Today gave the film three-and-a-half stars out of four, praising the film's conclusion: "the ending, though in part contrived, doesn't cop out".[7]

The soundtrack features several covers. The Cowboy Junkies' contribution to the soundtrack is a remake of a Robert Johnson song, while the Bad Brains and Henry Rollins track is a cover of the MC5 anthem. "Stand" by Liquid Jesus is a new version of the 1969 song by Sly & the Family Stone.

Peter Murphy's exclusive track was later included on a special reissue of his 1988 album, Love Hysteria, while Sonic Youth's song appeared on their 1990 release, Goo.

An earlier version of Soundgarden's "Heretic" appears on the 1985 Seattle band compilation album Deep Six. Concrete Blonde revisited "Everybody Knows" on their 2003 album, Live in Brazil. The original, upbeat version of "Wave of Mutilation" appears on Doolittle, the third studio album by Pixies.

A number of songs prominently featured in the film did not appear on the officially released soundtrack, including the original version of "Everybody Knows" by Leonard Cohen, which appeared on his 1988 album, I'm Your Man. Although Cohen's version serves as the theme song for Mark's pirate radio program during most of the film, he opens his final broadcast with the Concrete Blonde cover that appears on the soundtrack. Another Cohen song appears briefly when Mark is talking about Malcom's suicide on the air. The song is "If It Be Your Will" from Cohen's 1984 release Various Positions. Also present in the film but absent from the soundtrack are "Hello, Dad, I'm in Jail" by Was (Not Was) from their 1988 album What Up, Dog?, "Fast Lane" by Urban Dance Squad from their 1990 album Mental Floss for the Globe, "Weinerschnitzel" by The Descendents from their 1981 EP Fat, "Love Comes in Spurts" by Richard Hell and the Voidoids from their 1977 album Blank Generation, and "Talk Hard" by Stan Ridgway, the original version of which has never been released (though Ridgway has released a live version of the song). "Girls L.G.B.N.A.F." by Ice-T is played on a boombox outside of the school by some boys.

Not as prominently featured is a legendary early track by the Beastie Boys entitled "The Scenario". Although the song appears only briefly in Pump Up the Volume, it is notable because it never appeared in any official release, however is available on hard to find bootleg recordings. The song was cut from the Beastie's Def Jam album Licensed to Ill after being deemed too explicit. Christian Slater's character explains this when he introduces it on the air saying, "Now here's a song from my close personal buddies, the Beastie Boys...a song that was so controversial they couldn't put it on their first album."